Field of the Invention
This application is directed to the field of hip replacement, and particularly to surgical tools and methods for guiding the preparation of the bones in connection therewith.
Description of the Related Art
Hip replacement surgery is common and getting more common by the year. One persistent issue with hip replacement is the relatively high incidence of poor placement of the cup and ball components of the prosthetic hip joint. For example, the cup is optimally placed in a specific alignment with a plane including a rim of the acetabulum of the pelvis. For several reasons an unacceptably high percentage of patients have the cup of the artificial hip joint out of alignment with this plane.
Unfortunately, misalignment can lead to dislocation of the hip as soon as within one year of the implantation procedure. This is particularly problematic because recovery from a hip procedure can take many months. Patients undergoing a revision so soon after the initial implantation will certainly be dissatisfied with their care, being subject to addition redundant surgery. Of course, all surgery carries some degree of risk. These poor outcomes are unsatisfactory for patients and surgeons and are inefficient for the healthcare system as a whole.
Also, in cup placement in total hip arthroplasty, the inclination and anteversion angles are with respect to the Anterior Pelvic Plane (defined as a plane created by the two anterior superior iliac spines (ASIS) and the pubic symphysis). While these anatomical features are visible/palpable while the patient is in a supine position, the majority of total hip replacements are accomplished via a posterolateral approach with the patient in some variation of a lateral position, in which most of these landmarks are not accessible or visible. Historically, navigation for posterior approach hip replacement has been accomplished by registering the anatomical features of the Anterior Pelvic Plane with the patient first in a supine position and, once this plane is recorded by the navigation computer, moving the patient to a lateral position in order to perform hip surgery—with navigation performed with respect to the directly registered Anterior Pelvic Plane. This approach to hip navigation is sub-optimal for surgical workflow because the extra movement of the patient from supine to lateral position takes more surgeon and staff time and requires breaking sterility and re-draping. This is one of the key reasons why hip navigation has failed to be adopted by most of the market.
Additionally, altered leg length is a common patient complaint arising from hip replacement surgery and has been a common cause of medical malpractice lawsuits that arise from hip replacement. Because part of the hip replacement procedure requires precise measurements of patient leg length and joint off-set that are frequently difficult to visualize utilizing conventional instrumentation, there are opportunities to improve the surgeon's performance of these measurements using computer technology.